Numerical Simulation Of The Filling Stage Of Micro-injection Molding In Slit Cavity

With the development of the Micro Electro Mechanical System (MEMS), micro-injection molding technology is developed and widely used in the micro-mechanical, micro-electronics, micro-optics , biomedical and many other fields now. However, because of the very small size and volume of micro-plastic parts, the flow behavior of polymer in the filling stage of micro-injection molding has many differences compared with that of the traditional injection molding, Therefore, the key factors affecting the qualities of micro-parts are different with that the factors in the traditional injection molding.The filling stage is the most important stage in the micro-injection molding process and influences the part quality and production efficiency of micro-injection molding directly. Therefore, it has great theoretical and practical significance for designing micro-injection mould, setting processing parameters reasonably and improving micro-plastic parts quality to investigate the melt flow behavior in the filling stage in the micro-scale cavity, especially the micro-scale effect on the flow behavior, build mathematical model and efficient numerical method, and implement the numerical simulation of filling stage in micro-injection molding.The objective of the paper is to analysis the main factors and to simulate the filling stage of the micro-injection molding process. The works and achievements are as following:1. The differences of the process characteristic between micro-injection molding and traditional injection molding were compared. The influence factors in the micro-injection process were analyzed systematically and the micro viscosity model and wall slip velocity model were introduced.2. The steady-state flow of polymer in slit cavity was analyzed. The effects of the micro-viscosity and wall slip and the comprehensively effect of two factors on steady-state flow were investigated, and the influence laws of the micro-viscosity and wall slip on the steady-state flow were analyzed.3. Based on the viscous fluid mechanics and the flow characteristics of micro-injection molding process, the reasonable simplification and hypothesis were introduced, the micro-scale viscosity model based on Eringen and Okada theory and the power-law wall slip model were adapted, and the mathematical model of the filling stage in slit micro-cavity was built. Numerical simulation of the filling stage of micro-injection molding was implemented using hybrid Finite Element/ Finite Difference/Control Volume method. The effects of the micro-viscosity and wall slip on the viscosity, velocity and pressure field of the melt in the cavity in filling stage were investigated. The simulation results indicate that the micro-viscosity has the effect of hindering the melt flow and wall slip has the effect of promoting the melt flow. The melt flow condition in the filling stage of micro-injection molding is determined by the combined effects of micro-viscosity and wall slip.